Image-forming device, and dimension measurement device

ABSTRACT

The purpose of the present invention is to provide an image forming device and the like that is capable of forming a proper integrated signal even when an image or a signal waveform is acquired from a pattern having the possibility of preventing proper matching, such as a repetition pattern, a shrinking pattern, and the like. In order to achieve the purpose, there is proposed an image forming device that forms an integrated image by integrating a plurality of image signals and that is provided with: a matching processing section that performs a matching process between the plurality of image signals; an image integration section that integrates the plurality of image signals for which positioning has been performed by the matching processing section; and a periodicity determination section that determines a periodicity of a pattern contained in the image signals. The matching processing section varies a size of an image signal area for the matching in accordance with a determination by the periodicity determination section.

TECHNICAL FIELD

The present invention relates to an image forming device or a dimensionmeasurement device that acquires an image or a signal waveform using amicroscope and the like, particularly to an image forming device or adimension measurement device that forms an image or a waveform byintegrating image signals or signal waveforms.

BACKGROUND ART

In a charged particle beam device such as represented by a scanningelectron microscope, a sample is scanned with a narrowly convergedcharged particle beam, obtaining desired information (such as a sampleimage) from the sample. In such a charged particle beam device,resolution is becoming increasingly higher year by year, resulting in anincrease in the observation magnification ratio required for the highresolution. Beam scan methods for obtaining the sample image include amethod where a plurality of images obtained by high speed scan areintegrated to obtain a final target image, and a method where a targetimage is acquired by a single low speed scan (image capture time for oneframe on the order of 40 msec to 80 msec). As the observationmagnification ratio is increased, the influence of drift of the field ofview on the acquired image becomes more serious. For example, in themethod where the target image is acquired by integrating the imagesignals obtained by high speed scan on a pixel by pixel basis (frameintegration), if there is a drift during image integration due to acharge-up or the like of the sample, pixels with a displaced field ofview would be integrated, resulting in the target image afterintegration being blurred in the drift direction. In order to decreasethe influence of drift, the number of integrated frames may be decreasedso as to shorten the integration time; however, this makes it difficultto obtain a sufficient S/N ratio.

In the method where the image is acquired by low speed scan, if there isa drift during image capturing, the image would be deformed by the flowof the field of view in the drift direction.

When a resist pattern with high sensitivity is irradiated with chargedparticles by a charged particle beam device, the resist may be shrunk(contracted) by the scientific attributes of the resist. In theaforementioned method where the final target image is acquired byintegrating a plurality of images obtained by high speed scan, if theshrinking occurs during image integration, pixels with a displaced edgeposition due to the shrinking would be integrated, resulting in ablurring at the edge of the target image after integration.

Patent Literature 1 discloses a technology where image deformation orposition displacement due to a drift in a plurality of images obtainedby the plurality of scans is detected by image matching, and a composedimage in which the position displacement is corrected based on thedetected image deformation or position displacement is generated.

CITATION LIST

Patent Literature 1: JP 2007-299768 A (corresponding to U.S. Pat. No.7,034,296)

SUMMARY OF INVENTION Technical Problem

Miniaturization and the like that have been achieved in semiconductordevices in recent years have led to narrower patterns and intervalsbetween them as objects for observation or measurement. Patterns inwhich a plurality of continuously similar patterns are arranged(repetition pattern) as the object for observation or measurement havebecome more common. In the case of such patterns, because of thearrangement of a number of similar patterns, when integration isattempted on the basis of the execution of matching between imagesignals as objects for integration, as disclosed in Patent Literature 1,for example, there is the possibility of matching at an erroneousposition, preventing appropriate execution of the integration process.

Further, some samples cause shrinking upon being irradiated with anelectron beam. As a result, if image signals for a plurality of framesare acquired for integration, the edge position may be shifted beforeand after the shrinking, thus also preventing proper integration of thesignals.

In the following, a description is given of an image forming device anda dimension measurement device with the purpose of forming a properintegrated signal even when an image or a signal waveform of a patternthat has the possibility of preventing proper matching, such as arepetition pattern or a shrinking pattern, is acquired.

Solution to Problem

According to an embodiment for achieving the objective, there isproposed an image forming device comprising an operating device thatforms an integrated image by integrating a plurality of image signalsobtained by a microscope, characterized in that the operating deviceincludes a matching processing section that performs a matching processbetween the plurality of image signals, an image integration sectionthat integrates the plurality of image signals for which positioning hasbeen performed by the matching processing section, and a periodicitydetermination section that determines a periodicity of a patterncontained in the image signals, wherein the matching processing sectionvaries a size of an image signal area for the matching in accordancewith a determination by the periodicity determination section.

According to another embodiment for achieving the objective, there isproposed an image forming device comprising an operating device thatforms an integrated image by integrating a plurality of image signalsobtained by a microscope, characterized in that the operating deviceincludes a matching processing section that performs a matching processbetween the plurality of image signals, an image integration sectionthat integrates the plurality of images for which positioning has beenperformed by the matching, and a displacement detection section thatdetects a displacement between the plurality of image signals, wherein:the displacement detection section selectively detects the displacementin a specific direction of the images; the image integration sectionselectively corrects the displacement in the specific direction; thedisplacement detection section selectively detects the displacement in adirection different from the specific direction with regard to theplurality of image signals of which the displacement in the specificdirection has been selectively corrected; and the image integrationsection forms the integrated image by selectively correcting thedisplacement in the direction different from the specific direction.

According to yet another embodiment for achieving the objective, thereis proposed a dimension measurement device comprising an operatingdevice that measures a dimension of a pattern formed on a sample basedon an integrated signal formed by integrating a plurality of signalwaveforms obtained by a microscope, characterized in that the operatingdevice includes a matching processing section that performs a matchingprocess between the plurality of signal waveforms, and a signalintegration section that integrates the plurality of signal waveformsfor which positioning has been performed by the matching process,wherein the matching processing section executes the matching such thatanother signal waveform shape is aligned with a certain signal waveform.

Advantageous Effects of Invention

According to the above configuration, a proper integrated signal can beformed even when an image or a signal waveform is acquired from apattern having the possibility of preventing proper matching, such as arepetition pattern, a shrinking pattern, and the like.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a scanning electron microscope.

FIG. 2 is a flow chart showing the steps for setting a search area bypattern periodicity determination.

FIG. 3 illustrates an example of a correlation value distribution resultobtained by taking the autocorrelation of a single frame image.

FIG. 4 illustrates histograms of correlation values acquiredone-dimensionally from a maximum correlation value detected position.

FIG. 5 illustrates a method for determining period data in a patternhaving periodicity other than a line shape.

FIG. 6 illustrates an example of optimization of a search range in apattern having periodicity.

FIG. 7 illustrates an example in which a drift of one-half period ormore is caused in a single scan in an optimized search range.

FIG. 8 illustrates an example of a GUI screen displayed on an imagedisplay device.

FIG. 9 is a flow chart of a drift correction method adapted for linepattern roughness measurement.

FIG. 10 illustrates an example of a drift in X- and Y-directions of animage acquired by scanning a line pattern with a charged particle beamin the X-direction.

FIG. 11 illustrates a detected drift amount and an example of fitting ofthe drift amount by an approximation curve.

FIG. 12 illustrates an example of correction of an X-direction positiondisplacement of a single frame image in a line pattern.

FIG. 13 illustrates an example of detection of a Y-direction positiondisplacement using the single frame image in which the X-directionposition displacement has been corrected.

FIG. 14 illustrates an example of correction of a Y-direction positiondisplacement of a line pattern using pattern roughness.

FIG. 15 is a cross sectional view of a line pattern, illustrating anexample of an electron microscope image.

FIG. 16 illustrates a profile of a line pattern after simple additionand a profile after weighted addition.

FIG. 17 is a flow chart of a method for creating an integrated imagewith a varied weight added to the profile for the latter period ofshrinkage.

FIG. 18 illustrates a profile of a line pattern in which an edgeposition displacement has been corrected.

FIG. 19 is a flow chart of a mode for creating a composed image in whichthe edge position is corrected by detecting an edge displacement betweenframes due to shrinkage.

FIG. 20 illustrates an example of a GUI screen for shrink edgecorrection displayed on an image display device.

FIG. 21 is a flow chart of a method for creating a composed image inwhich a position displacement is corrected by detecting a positiondisplacement due to drift and an edge position displacement due toshrinkage.

FIG. 22 illustrates an example of a method for detecting a drift amountwith reference to a pattern center as a reference position.

FIG. 23 illustrates the outline of an image forming system or adimension measurement system using a scanning electron microscope.

DESCRIPTION OF EMBODIMENTS

In the following, a device that forms a composed signal by integratingimage signals or signal waveforms for which positioning is performed bya matching process will be described in detail. Particularly, in thefollowing embodiment, an image forming device and a dimensionmeasurement device will be described that are suitable for forming animage or a signal waveform of a periodic pattern in which a plurality ofequivalent patterns are arranged, a shrinking pattern, or the like.

When matching is performed in a case where the object subjected tonormalized correlation is an image displaying a periodic pattern, aplurality of locations exist where matching scores equivalent to that ofa location that is originally intended for positioning are exhibited. Asa result, there is the possibility of an erroneous detection during thedetection of the amount of position displacement between images unlessan appropriate search area is set.

For example, if an erroneous detection occurs, a wide area of unevencontrast may be produced in a composed image composed of images based onthe detected positions. Thus, there is the possibility that themeasurement accuracy may be decreased in the area having the unevencontrast in the composed image.

Further, if a drift based on charge-up is caused in a line pattern, acomposed image in which even roughness is recognized cannot be obtainedafter position displacement correction unless a position displacement inthe horizontal direction with respect to the pattern is detected withhigh accuracy during the detection of the position displacement betweenimages. Because the feature amount for determining a matching score issmall in the horizontal direction with respect to the line pattern edge,it is difficult to detect the position displacement with high accuracy.Accordingly, when it is desired to measure even roughness of a linepattern in a composed image to which drift correction technology isapplied, there is the possibility of a decrease in measurement accuracy.

Further, if the shrinking occurs during image capturing due to theinfluence of charged particle beam scan, the edge positions that are tobe measured may be displaced when added during frame integration,resulting in a blurring in the composed image edge. Thus, in the methodwhere the final target image is obtained by integrating a plurality ofimages, there is the possibility of a decrease in the measurementaccuracy of the composed image.

An embodiment described below solves a new problem encountered duringsignal integration which is caused by the transition semiconductordevices have gone through in recent years, and relates to an imageforming device and a dimension measurement device that achievesuppression of a displacement in the field of view with high accuracywhile suppressing the influence of charging or shrinkage due to chargedparticle beam irradiation.

The embodiment described below relates to a device in which, using asample image forming method by which a sample is scanned with a chargedparticle beam and an image is formed based on a secondary signal emittedfrom the sample, a plurality of composed images are formed by composinga plurality of images obtained by a plurality of scans, and the imagesare composed while correcting a position displacement between theplurality of composed images, thus forming a further composed image. Thedevice is thus capable of forming with high accuracy an image or asignal waveform of a pattern having a feature that has the possibilityof decreasing matching accuracy, such as a periodic pattern, a linepattern, a shrinking pattern, and the like.

FIG. 1 is a schematic configuration diagram of an image forming deviceor a dimension measurement device, or a scanning electron microscopeconstituting a part thereof. Between a cathode 1 and a first anode 2, avoltage is applied from a high-voltage control power supply 20controlled by a computer 40, whereby a primary electron beam 4 is drawnfrom the cathode 1 with a predetermined emission current. Between thecathode 1 and a second anode 3, an acceleration voltage is applied fromthe high-voltage control power supply 20 controlled by the computer 40,whereby the primary electron beam 4 emitted from the cathode 1 isaccelerated before proceeding to lens systems in subsequent stages.

The primary electron beam 4 is converged by a converging lens 5controlled by a lens control power supply 21 and has an unwanted regionof the primary electron beam removed by an aperture plate 8. The beam isthen converged on a sample 10 as a fine spot by a converging lens 6controlled by a lens control power supply 22 and an objective lens 7controlled by an objective lens control power supply 23. The objectivelens 7 may have various modes, such as an in-lens mode, an out-lensmode, or a snorkel mode (semi-in-lens mode). A retarding mode where anegative voltage is applied to the sample to decelerate the primaryelectron beam is also possible. Each of the lenses may be composed of anelectrostatic lens composed of a plurality of electrodes.

The primary electron beam 4 is caused to scan the sample 10 twodimensionally (in the X-Y directions) by a scan coil 9. The scan coil 9is supplied with current by a scan coil control power supply 24. Asecondary signal 12, such as a secondary electron emitted from thesample 10 due to the primary electron beam irradiation, travels over theobjective lens 7. The secondary signal 12 is separated from a primaryelectron by an orthogonal electromagnetic field generating device 11 forsecondary signal separation, and then detected by a secondary signaldetector 13. The signal detected by the secondary signal detector 13 isamplified by a signal amplifier 14, transferred to an image memory 25,and then displayed on an image display device 26 as a sample image. Thesecondary signal detector may be configured to detect a secondaryelectron or a reflected electron, or configured to detect light or anX-ray.

An address signal corresponding to a memory position in the image memory25 is generated in the computer 40, and, after analog conversion,supplied via the scan coil control power supply 24 to the scan coil 9.When the image memory 25 has 512×512 pixels, for example, an X-directionaddress signal is a digital signal repeating 0 to 511. A Y-directionaddress signal is a digital signal repeating 0 to 511 which isincremented by one when the X-direction address signal reaches from 0 to511. The digital signals are converted into analog signals.

Because the address in the image memory 25 corresponds to the address ofthe deflecting signal for primary electron beam scan, a two-dimensionalimage of an area in which the primary electron beam is deflected by thescan coil 9 is recorded in the image memory 25. The signals in the imagememory 25 can be read successively in chronological order by a readaddress generation circuit (not shown) synchronized by a read clock. Thesignals read in accordance with the address are converted into analogsignals, providing a brightness modulation signal for the image displaydevice 26.

The image memory 25 is provided with the function for storing images(image data) for S/N ratio improvement in an overlapped (composed)manner. For example, a single completed image is formed by storingimages obtained by eight two-dimensional scans in an overlapped manner.Namely, a final image is formed by composing images formed by one ormore units of X-Y scan. The number of images for forming a singlecompleted image (frame integration number) may be arbitrarily set, andthus a proper value is set in view of conditions such as secondaryelectron generation efficiency. It is also possible to form an imagethat is desired to be finally acquired by further overlapping aplurality of images formed by integrating a plurality of images. Primaryelectron beam blanking may be executed when or after a desired number ofimages has been stored, so as to interrupt the input of information tothe image memory.

When the frame integration number is set to 8, there may be provided asequence such that the first image is erased upon input of a ninthimage, resulting in eight remaining images. It is also possible toperform weighted averaging such that, when a ninth image is input, theintegrated image stored in the image memory is multiplied by ⅞ and theninth image is added to the resultant image.

Two stages of deflecting coil 51 (image shift deflector) are disposed atthe same position as that of the scan coil 9, so that the position(observation field of view) of the primary electron beam 4 over thesample 10 can be two dimensionally controlled. The deflecting coil 51 iscontrolled by a deflecting coil control power supply 31.

The stage 15 can move the sample 10 in at least two directions (theX-direction and the Y-direction) in a plane perpendicular to the primaryelectron beam.

Via the input device 42, image capturing conditions (scan speed, numberof integrated images), the field of view correction mode, and the likecan be designated. Also, image output or save and the like may also bedesignated.

The device illustrated in FIG. 1 is provided with the function offorming a line profile on the basis of the detected secondary electronor reflected electron, for example. The line profile is formed on thebasis of the amount of electron detected during one- or two-dimensionalscan of the primary electron beam, sample image brightness information,and the like. The obtained line profile is used for dimensionmeasurement of the pattern formed on the semiconductor wafer, forexample. The device according to the present embodiment may be furtherprovided with an interface 41 for transferring image data to an externaldevice or the like, or with a recording device 27 for storing image datain a predetermined storage medium.

While FIG. 1 is described on the assumption that the control device isintegral or virtually integral with the scanning electron microscope,the present invention is not limited to such embodiment. For example, acontrol processor provided separately from the scanning electronmicroscope body may perform a process as will be described below. Inthis case, there will be required a transmission medium for transmittinga detection signal detected by the secondary signal detector 13 to thecontrol processor or for transmitting a signal from the controlprocessor to the lenses, deflector, and the like of the scanningelectron microscope, and an input/output terminal for the input andoutput of signals transmitted via the transmission medium.

A program for performing a process which will be described below may beregistered in the storage medium, and the program may be executed by thecontrol processor having an image memory and supplying required signalsto the scanning electron microscope. Namely, the embodiment which willbe described below may be implemented in the form of a program that canbe adopted in the charged particle beam device of the scanning electronmicroscope and the like provided with an image processor.

FIG. 23 illustrates a mode of the image forming device or dimensionmeasurement device including the scanning electron microscope. Thepresent system includes an SEM body 2301, an A/D converter 2304, anoperating device (including a signal processing device 2306 forperforming an image process) 2305.

The SEM body 2301 irradiates a sample, such as a wafer with anelectronic device produced thereon, with an electron beam, captureselectrons emitted from the sample with a detector 2303, and converts thesignal into a digital signal in the A/D converter 2304. The digitalsignal is input to the operating device 2305 and stored in a memory2307. An image process for the particular purpose is performed by imageprocessing hardware in the signal processing section 2306, such as aCPU, an ASIC, or an FPGA. The signal processing section 2306 is alsoprovided with the function of creating a line profile on the basis ofthe detection signal and measuring a peak-to-peak dimension of theprofile.

The operating device 2305 is further connected to an input device 2315including an input means, and has the function of causing a displaydevice of the input device 1108 to display an image, an inspectionresult, or the like for the operator.

The controls or processes in the operating device 2305 may be partly orentirely assigned to an electronic computer or the like provided with aCPU and a memory for storing images for processing or control. The inputdevice 2315 also functions as an image recipe creation device forcreating, either manually or by utilizing electronic device design data,an image recipe including the coordinates of an electronic devicerequired for inspection, pattern matching templates used forpositioning, photography conditions, and the like.

The input device 2315 is provided with a template creation section forcreating a template by cutting out a part of a diagram image formed onthe basis of design data. The created template is registered in thememory 2305 as a template for template matching in a matching processingsection 2306 contained in the signal processing section 2306. Templatematching is a technique for identifying locations where a photographedimage as the object for positioning and the template are aligned witheach other on the basis of coincidence degree determination usingnormalized correlation process, for example. The matching processingsection 2308 identifies a desired position of the photographed image onthe basis of the coincidence degree determination.

A signal integration section 2309 integrates the signals beforeintegration that are registered in the memory 2307 or acquired by thescanning electron microscope. A periodicity determination section 1310analyzes the frequency component of the acquired image or signalwaveform by autocorrelation method or the like. The periodicitydetermination section 1310 determines periodicity with respect tospecific directions (the X-direction, the Y-direction) and, upondetermining that there is periodicity, transmits the determinationresult to the matching processing section 1308.

In the matching processing section 1308, a size of an image area formatching is set on the basis of the determination result and theconditions stored in the memory 2307. For example, when it is determinedthat there is no periodicity, a pre-stored size of image area, or animage area greater than the pre-stored image area is selected. On theother hand, when it is determined that there is periodicity, apre-stored size of image area, or an image area smaller than thepre-stored image area is selected. Thus, when it is determined thatthere is periodicity, a relatively small image area is set. Preferably,when it is determined that there is periodicity, the size of the imagearea may be limited to a range such that two or more patterns of thesame shape are not included, so that the image area does not include aplurality of locations suspected of having a high matching score.Preferably, in the absence of periodicity, the image area may berelatively widened so as to enable matching using an image areaincluding a more complex pattern shape.

A displacement detection section 1311 detects a displacement in aspecific direction using an autocorrelation method, for example. Forexample, in the case of a line pattern extending in the Y-direction,when a brightness distribution (profile waveform) in the X-direction isdetected, a peak is present at an edge portion. Thus, the amount ofdisplacement is evaluated by performing autocorrelation between awaveform acquired in a certain frame and a waveform acquired at adifferent timing. In the case of the line pattern, when a displacementin the X-direction is detected, noise component can be decreased byadding signal waveforms of different positions in the Y-direction andaveraging them. Further, when a displacement in the Y-direction isdetected, a waveform indicating the frequency component of roughness ofa pattern at an edge portion may be formed, and a displacement betweenwaveforms acquired in different frames may be determined by mutualcorrelation method.

In the embodiment described below, a control device mounted in the SEM,or a control device (input device 1315) connected to the SEM via acommunication line and the like will be described by way of example.However, this is not a limitation, and the processes described below maybe performed using a general-purpose operating device that executes animage process in accordance with a computer program. Further, thetechnique described below may be applied to other charged particle beamdevices, such as a focused ion beam (FIB) device.

Embodiment 1

In an embodiment directed to a method for improving S/N ratio byintegrating TV scan images, a process flow of FIG. 2 will be describedbelow. In the present embodiment, by adopting the technique describedbelow when a TV scan image has a position displacement due to a drift,it becomes possible to optimize a search range on the basis of thepattern shape, structure, or the like of the TV scan image, and todetect the position displacement and generate a composed image in whichthe position displacement is corrected. The following process isexecuted by the computer 40 or the operating device 2305, for example.

First Step (S2001):

A frame integration number N is designated via the input device 42.

Second Step (S2002):

When an instruction for starting image capture is entered via the inputdevice 42, the frame integration number N of single frame images F (F1,F2, F3, . . . , FN) are continuously acquired from the same field ofview and set in a memory area.

Third Step (S2003):

As illustrated in FIG. 3, the autocorrelation of the single frame imagedata 3001 is taken to acquire a correlation value distribution 3002 ofthe single frame image. The peak (maximum value) of the correlationvalues at a detection position 3003 where the correlation value is highis utilized for pattern shape or periodicity determination.

Fourth Step (S2004):

Pattern shape determination is performed on the basis of the correlationvalue data acquired in the third step. First, a histogram of correlationvalues in the horizontal and vertical directions from the highestcorrelation value detected position is created. In the createdhistogram, if the data is concentrated in a specific section asillustrated in FIG. 4, it is determined that a line shape is exhibitedin the detection direction.

If it is determined that either the X- or Y-direction is the line shape,the process of a fifth step is performed. If it is determined that theline shape is not in the X- or Y-direction, the process of a seventhstep is performed.

Fifth Step (S2005)

In the case of a line shape, periodicity determination is performed.From the highest correlation value detected position, correlation valuesare one-dimensionally acquired with respect to a direction that was notdetermined to be the line shape, and the peak (maximum value) of thecorrelation values is calculated. For example, in the case of a verticalline pattern, the X-direction correlation values are acquired. In thecase of a horizontal direction line pattern, the Y-direction correlationvalues are acquired.

The acquired correlation values are filtered by a certain specificthreshold value, and the peak of the correlation values is calculated.If there is a plurality of peaks, it is determined that there isperiodicity. If there is one peak of the correlation values, it isdetermined that there is no periodicity.

Sixth Step (S2006)

If it is determined that the pattern is a line shape and there isperiodicity, peak-to-peak distances of the correlation values areaveraged to provide period data.

Seventh Step (S2007)

In the case of a pattern other than a line shape, periodicitydetermination is performed. The correlation values acquired from thecorrelation distribution data 3002 of FIG. 3 are filtered by a certainspecific threshold value, and it is determined if there is a correlationvalue peak (maximum value). If there is a plurality of correlation valuepeaks, it is determined that there is periodicity. If there is onecorrelation value peak, it is determined that there is no periodicity.

Eighth Step (S2008)

If it is determined that the pattern is other than a line shape andthere is periodicity, the position of detection of the peak of acorrelation value 5002 positioned at a shortest distance excepting thepeaks of the correlation values in the horizontal direction and thevertical direction is acquired from a detection position 5001 with thehighest correlation value as illustrated in FIG. 5. A distance 5003between the two points is resolved into an X-direction component 5004and a Y-direction component 5005, thus providing X-direction andY-direction period data.

Ninth Step (S2009):

If it is determined in the fifth step or the seventh step that there isperiodicity in the pattern structure, the acquired X- and Y-directionperiodicity data is set as a drift amount search range, as illustratedin FIG. 6. If the periodicity data calculated in the sixth step or theeighth step is set as the search range as is, an adjacent pattern may bedetected. Thus, a slightly narrowed range of periodicity data is set asthe search range.

If it is determined in the fifth step or the seventh step that there isno periodicity in X- or Y-direction, a default value is set in thesearch range. The search range may be set to an arbitrary value set bythe user.

Tenth Step (S2010):

The search range calculated in the ninth step is set, and the amount ofposition displacement is detected based on a combination of adjacentsingle frame images F(n−1) and F(n). The amount of position displacementin pattern detection may be calculated from normalized mutualcorrelation and the like.

The detected amount of position displacement is accumulated with theamount of position displacement with respect to a reference image as theobject for integration. A detection method adapted for the informationof the pattern shape determined in the fourth step may be adopted.

Eleventh Step (S2011):

A single frame image in which the amount of position displacement fromthe reference image as calculated in the tenth step is corrected isgenerated and added to the reference image, generating an integratedimage.

Twelfth Step (S2012):

The tenth step and the eleventh step are repeated until the frameintegration number N is reached.

In the present embodiment, when one half period or more of drift occursin a single electron beam scan by low speed scan or the like, asillustrated in FIG. 7, pattern detection is performed in the optimizedsearch range. When a number of patterns are measured at once althoughthe composed positions may differ from the actual pattern, measurementresults from a plurality of patterns are often averaged. Thus, noproblem would be caused in the measurement result even if the overlappedposition is displaced by one period.

The device according to the present embodiment also provides a mechanismfor entering input settings of correction object pattern shape,structure, and position displacement search range as prior informationof the selection of the necessity 0801 of applying the image driftcorrection technology or drift correction application on a graphicaluser interface (GUI), so that the application of the drift correctiontechnology can be chosen by the operator as illustrated in FIG. 8. Whena pattern shape 0802, a structure 0803, and search range information0804 are set on the GUI in advance, the third to eighth steps of thepresent embodiment may be omitted.

FIG. 11 illustrates an example in which the selections are made using apointing device 0805 or the like on the image display device. However,this is not a limitation, and the settings may be made using other knowninput setting means.

Embodiment 2

An embodiment will be described in which the drift correction technologyis applied when an image acquired by a particle beam scan in theX-direction in a vertical line pattern is drifted in the X- andY-directions. The present embodiment will be described with reference toa process flow of FIG. 9, and a supplementary description will be givenwith reference to FIGS. 10 to 13.

First Step (S0901):

N images such that sufficient pattern S/N can be obtained are acquiredon a frame by frame basis.

Second Step (S0902):

The amount of drift in the X-direction is detected using an (n−1)thframe image and an (n)th frame image.

When there is the influence of drift, the line pattern may appeardeformed, as illustrated in FIG. 10. If the Y-direction drift detectionis performed with such image, pattern detection would be subject to theinfluence of drift. Thus, in the first step, the amount of displacementonly in the X-direction is detected. The amount of drift may becalculated from the amount of position displacement in patterndetection. The amount of position displacement in pattern detection maybe calculated from a normalized mutual correlation or the like.

In order to determine an approximation curve from the cumulative totalof the drift amount, a cumulative total of a drift amount Δx in theX-direction up to (n)th frame is calculated. When the drift amount Δx inthe X-direction has been calculated for N frames, Δx is fitted by theapproximation curve. FIG. 11 shows a graph of the drift amount and itsapproximation curve. When the drift is due to the influence of charging,a tendency is such that the drift amount is large immediately after thestart of image acquisition and then gradually converges thereafter.Thus, the approximation curve can be approximated using logapproximation or polynomial approximation.

Third Step (S0903):

From the approximation curve of Δx, a corrected image for the first to Nframes corrected in the X-direction is generated. As illustrated in FIG.12, by performing correction in the X-direction, the drift occurring ina single frame can be corrected, while the Y-direction correctionenables correction well utilizing the pattern roughness.

Fourth Step (S0904):

Thereafter, the amount of drift in the Y-direction is detected using thecorrected image for the N frames in which the X-direction drift has beencorrected, as illustrated in FIG. 13. As in the X-direction, acumulative total of the drift amount is calculated in advance for theY-direction. After the detection of the drift amount for the N-th frameis completed, the cumulative total of the drift amount is fitted by anapproximation curve, as in the X-direction.

Fifth Step (S0905):

A composed image composed of N frames is generated while the drift inthe Y-direction is corrected on the basis of the approximation curvedetermined as illustrated in FIG. 14, and then the process ends. Thus,the X-direction and the Y-direction are corrected separately, wherebythe Y-direction can also be accurately corrected by utilizing thepattern roughness.

Embodiment 3

An embodiment will be described in which an edge position displacementof an integrated image is caused by shrinkage in the method forimproving the S/N ratio by integrating the TV scan image.

By modifying the weighting during frame integration, the influence ofedge blurring due to shrinkage is reduced. It is also possible to createa composed image in which the edge position is corrected by detecting anedge displacement between individual frames.

With reference to FIG. 15 and FIG. 16, a system for modifying the addedweight during frame integration will be described. FIG. 15 is a crosssectional view of a semiconductor line pattern, illustrating an exampleof an electron microscope image. A resist line pattern 1502 formed on asubstrate 1501 and having an edge 1503 is observed as a pattern portion1512 and an edge portion 1513 in the electron microscope image. Theelectron microscope image 1511 is an image of the line pattern 1502 asobserved from above.

When a dimension of the line pattern of FIG. 15 is measured, a profileas illustrated in FIG. 16 is created from the electron microscope image1511, and then a characteristic position, such as a differential peak ofthe edge portion 1513, is captured. Generally, a method is employedwhere the characteristic position is detected with respect to the leftand right edges, and their distance is determined as a patterndimension. A profile obtained in a pattern from which shrinking occursprovides a simple additional profile 1604 based on the addition of aprofile 1601 for the initial period of shrinking and a profile 1602 forthe latter period of shrinking. When the dimension is measured in suchprofile, the edge portions of the profile become blurred, destabilizingthe characteristic position and decreasing measurement reproducibilityas well.

FIG. 17 illustrates a flow for creating an integrated image of a profile1603 in which the added weight is varied between the profile 1601 forthe initial period of shrinking and the profile 1602 for the latterperiod of shrinking. In the following, each step will be described.

First Step (S17001):

When image acquisition is started, a single frame image is captured intothe image memory 25.

Second Step (S17002):

A line profile is created by the computer 40.

Third Step (S17003)

A characteristic position is detected from the obtained profile as anedge, and information of its position is stored in the computer 40.

Fourth Step (S17004)

The process of S17001 to S17003 is repeated for the designated number offrames.

Fifth Step (S17005)

The amount of displacement in the edge positions between the respectiveframes is calculated from the edge position of each frame, and the totalamount of displacement is divided by the amount of displacement betweenthe respective frames, providing a weight. Namely, the weight W(x) ofeach frame is expressed by the following expression.W(x)=St/S(x)  (1)where St is the total amount of displacement and S(x) is the amount ofdisplacement between the respective frames.

It is known that the amount of shrinking changes exponentially. In thiscase, expression (1) can be expressed, using the designated number N ofadded frames, as follows:W(x,N)=(2x+1)/(N(N+2))  (2)Sixth Step (S17006):

When frame addition is implemented by multiplying the weight accordingto expression (1) or expression (2) by each frame image, an integratedimage that takes the shrinking amount into consideration can beobtained. With regard to the weight W(x), an empirically determinedarbitrary value may be used.

Next, a system for creating a composed image in which the edge positionis corrected by detecting an edge displacement between frames will bedescribed. As illustrated in FIG. 18, profiles obtained from a patternin which shrinking occurs are almost identical in shape, such as aprofile 1801 for the initial period of shrinkage and a profile 1802 forthe latter period of shrinkage. However, the shape is shrunk from thecenter of the pattern. Thus, the shape is divided into left and rightportions by determining a center of gravity 1803 of the profile 1801 forthe initial period of shrinkage. With respect to the left and right edgeprofiles, correlation values with the profile 1802 for the latter periodof shrinkage are computed, and the profiles are overlapped at positionswith the highest correlation value. Alternatively, the highest positionsor differential peaks of the profiles may be aligned. By finding anarithmetic mean of the aligned left and right edges, a line profile 1804is obtained. Similarly, the alignment may be with the profile for theinitial period of shrinkage. The above flow will be described withreference to FIG. 19.

First Step (S19001):

When image acquisition is started, a single frame image is captured intothe image memory 25.

Second Step (S19002):

A line profile is created by the computer 40.

Third Step (S19003):

An edge position and the center of gravity of the obtained profile arecomputed.

Fourth Step (S19004):

Information of the position and the center of gravity is stored in thecomputer 40.

Fifth Step (S19005):

Then, the amount of displacement from the profile of a preceding framethat has been stored is calculated to shift the edge position.

Sixth Step (S19006):

The process from S19001 to S19005 is repeated for the designated numberof frames.

Seventh Step (S19007):

The frame images with the shifted left and right edges are averaged toprovide a composed image.

The device according to the present embodiment is also provided with amechanism enabling the selection of the necessity 2001 of application ofshrink edge correction on a graphical user interface (GUI), so that theoperator can choose to apply the shrink edge correction, as illustratedin FIG. 20. A setting in combination with a drift correction 2002 isalso possible. While FIG. 20 illustrates the example allowing theselections using a pointing device 2003 and the like on an image displaydevice, this is not a limitation, and the settings may be made usingother known input setting means.

Embodiment 4

An embodiment in which a position displacement of an image having adrift and shrinking is corrected by drift correction technology will bedescribed. In this example, when a composed image is generated byintegrating TV scan images using a resist pattern that causes a driftdue to charge-up, the composed image is influenced by the positiondisplacement due to the drift and shrinkage, resulting in a significantdecrease in measurement accuracy. The process flow of the presentembodiment is illustrated in FIG. 21 and will be described below.

First Step (S21001):

When image acquisition is started, a single frame image is captured intothe image memory 25.

Second Step (S21002):

A reference position for the pattern of the single frame image isacquired. As the reference position, a position that is not subject tothe influence of shrinkage is set. For example, when shrinkage occurs,although the edges may become contracted from the pattern center, thepattern center position is not varied. Thus, the reference position maybe the center of the pattern or the center of gravity. A line profilemay be created, and the center of gravity of the profile may be set asthe reference position.

Third Step (S21003):

The amount of displacement in reference position between the singleframe images is calculated. The detected amount of position displacementis accumulated with the amount of position displacement from the firstframe image. In a pattern illustrated in FIG. 22 where a drift and anedge shrinking have occurred in the single frame image acquired by aplurality of scans, it is determined how much the reference position hasbeen shifted.

Fourth Step (S21004):

After the position displacement of the reference position is calculated,a single frame image in which the position displacement is corrected iscreated.

Fifth Step (S21005):

A line profile of the corrected image is created by the computer 40.

Sixth Step (S21006):

The edge position and the center of gravity of the obtained profile arecomputed. Information of the position and the center of gravity isstored in the computer 40.

Seventh Step (S21007):

Then, the amount of displacement from the profile of the preceding framethat has been stored is calculated to shift the edge position.

Eighth Step (S21008):

The process from S21005 to S2107 is repeated.

Ninth Step (S21009):

The frame images with the left and right edges shifted as describedabove are averaged, obtaining a composed image.

REFERENCE SIGNS LIST

-   1 Cathode-   2 First anode-   3 Second anode-   4 Primary electron beam-   5, 6 Converging lens-   7 Objective lens-   8 Aperture plate-   9 Scan coil-   10 Sample-   11 Orthogonal electromagnetic field generating device-   12 Secondary signal-   13 Secondary signal detector

The invention claimed is:
 1. A charged particle beam device comprising aprocessor that forms an integrated image by integrating a plurality ofimage signal regions obtained by scanning a semiconductor device with acharged particle beam, wherein the processor includes: a matchingprocessing section that performs a matching process between theplurality of image signal regions; an image integration section thatintegrates the plurality of image signal regions for which positioninghas been performed by the matching processing section; and a periodicitydetermination section that determines a periodicity of a patterncontained in the image signal regions for which an image integration isperformed by the image integration section wherein the patternconfigures a circuit of the semiconductor device, wherein theperiodicity determination section determines whether the patternincluded in the image signal regions is a pattern having a periodicityin one direction, or a pattern having periodicities in pluraldirections, by using autocorrelation for the image signal regions, andwhen the pattern has a periodicity in one direction, periodicity data ofthe one direction is obtained, and when the pattern has periodicities inplural directions, periodicity data of the plural directions isobtained, wherein the matching processing section narrows a search rangeof the matching in the one direction or in the plural directions, sothat the periodicity of the pattern contained in the plurality of imagesignal regions disappears in accordance with a determination by theperiodicity determination section, and calculates an amount of driftbased on the matching process in the search range, and the imageintegration section amends the amount of drift, and integrates signalsin the plurality of image signal regions.
 2. The image forming deviceaccording to claim 1, wherein: the periodicity determination sectiondetermines the presence or absence of the periodicity of the pattern;and the matching processing section executes the matching by narrowing apredetermined image signal area when it is determined that there isperiodicity in the pattern.
 3. The image forming device according toclaim 1, wherein the periodicity determination section determines theperiodicity based on an autocorrelation process of the image signalsobtained by the microscope.
 4. The image forming device according toclaim 1, wherein the periodicity determination section determineswhether the pattern is present in a predetermined period.